Sintered hard metal composition



Patented July 25, 1939 UNITED PATENT F FC Floyd 0. Kelley, Schenectady, N. Y., asslgnor to General Electric Company, a. corporation of New York No Drawing. Application January 20, 1933, Serial No. 652,689

1 Claim.

The present application is a continuation in part of my application Serial No. 496,826, filed November 19, 1930, and relates to sintered, hard, tough, metal compositions generally known as 5 cemented carbides. Compositions of this general character are disclosed in the Schroter Reissue Patent No. 17,624 and Schroter Patent No. 1,721,416, and may consist of a carbide of an element of the sixth group of Mendelyeevs table of elements of the periodic system, for example tungsten carbide and a binder material having a lower melting point than the carbide, for example metal of the iron group such as cobalt, the latter acting as a cementing or binder medium for the tungsten carbide particles in the composition.

It is one of the objects of the present invention to provide a hard, tough, cemented carbide tool which may be shaped or ground easily and supplied with a keen cutting edge by means of ordinary grinding wheels. A further object of the invention is to provide a metal cutting tool in which cratering action caused by metal chips from the work striking the tool back of its cutting edge, is substantially eliminated. Another object of the invention is the provision of a metal cutting tool having a low coeflicient of friction. Other objects of the invention will appear hereinafter.

In carrying out my invention, I employ a carbide of metal of the fifth group of Mendelyeevs table of elements of the periodic system such as tantalum carbide with a carbide of an element of the sixth group of Mendelyeevs table of elements of the periodic system, for example tungsten carbide (WC) as the main constituents of the sintered composition, the binder or cementing material for the carbides comprising from about 3% to about 20% of the composition.

The element columbium is practically always present in tantalum ores in varying quantities and is very diflicult to remove therefrom. It will be understood therefore that in the present composition a portion of the tantalum carbide may be replaced by columbium carbide.

The tantalum carbide may be prepared by adding about 12 grams of carbon, for example gas coke, to about 181.5 grams of tantalum and milling the tantalum and carbon together for about five hours. The milling produces a very intimate mixture of the materials which may then be fired at a temperature varying from about 1550 to 1600 C. for about eight hours in a. closed graphite tube and in a hydrogen furnace. A similar carburizing process is disclosed in my copending application Serial No. 308,565, filed September 26,

1928. The tungsten carbide may be prepared in the same manner as the tantalum carbide.

Both carbides are usually milled to break them up into a fine powder capable of passing through a 325 mesh screen. The carbides, in any desired 5 ratio, are then mixed with a suitable amount of binder material, for example with about 3% to about 20% of binder metal having a lower melting point than either of the carbides and pressed into any desired shape in a hydraulic press. The 10 pressed material is then sintered in a closed graphite tube in a hydrogen furnace at a temperature of about 1400 C. for about 1 /2 hours.

The final sintered product is usually in the form of tool bits which may be secured to supl5 porting shanks by any of several well known processes, for example by copper brazing. If the bits are copper brazed to steel shanks, it is desirable to employ a flux, such as borax, in the brazing operation. 20

A cemented carbide having a composition containing about 13% cobalt and about 87% of a 50/50 mixture by weight of tantalum carbide and tungsten carbide, has a hardness of about 86.4 on a Rockwell A scale and a modulus of rupture of 25 about 205,000 pounds per square inch. The latter figure may be obtained on tool bits as fired and without previous lapping.

The ratio of tantalum carbide to tungsten carbide may vary widely. For example, in sintered 30 compositions containing about 3% to about 20% of binder material the remainder of the composition may consist of about 10% to about 90% tungsten carbide and about 90% to about 10% tantalum carbide. In other words, such compositions 35 may consist of about 87.3% to about 8% tungsten carbide, about 8% to about 87.3% tantalum carbide and from about 3% to about 20% of a binder material. Particularly satisfactory results have been obtained with the following compositions: go

70% tungsten carbide 21% tantalum carbide 9% cobalt tungsten carbide 27% tantalum carbide 13% cobalt tungsten carbide 24% tantalum carbide 6% cobalt 54% tungsten carbide 40% tantalum carbide 6% cobalt 43.5% tungsten carbide 43.5% tantalum carbide13% cobalt I prefer to employ cobalt as the binder or ce- 45 menting medium for the carbides. My invention however is not limited to any specific binder material. Any element of the iron group, combinations of elements of the iron group, or manganese may be employed as binder material. Also, if 60 desired, various combinations of metal of the iron group with other metals may be employed as the binder material for the carbide particles in the composition, for example binders consisting of about 70% to 95% cobalt with about 30% to about tungsten carbide and binders containing from about 90% to about metal of the iron group with about 10% to about 90% of metal of the sixth group of Mendelyeevs Periodic Table of elements.

In the sintering operation a portion of the carbides maybe dissolved in the binder material so that while a binder may consist, for example substantially of cobalt, it will be understood that it may also contain a certain percentage of tantalum carbide and tungsten carbide dissolved in the cobalt.

Although I prefer to manufacture the present composition in the manner disclosed in 'the Schroter reissue patent and the Schroter patent, my invention is not limited to this process since the powdered materials comprising the composition may be hot pressed in the manner disclosed in Hoyt Patent No. 1,843,768 or Gilson Patent No. 1,756,857.

A cemented carbide composition containing about 3% to about 20% of a binder material, the remainder consisting of tungsten carbide and tantalum carbide, has a low coefficient of friction. Such compositions are usually employed in the form of tool bits copper brazed to supporting steel shanks. Owing to the low coefficient of friction of the cemented carbide a relatively small amount of heat is generated during operation of the tool and there is no tendency for the brazing metal to soften or for the tool bit to become loosened. The low coeflicient of friction of the cemented carbide also results in a low consumption of power during operation of such tools.

Cemented carbide tools having the compositions noted above may be given a very sharp edge which may be retained under severe operating conditions. The ability to retain a sharp cutting edge permits the production of work which has an unburnished, smooth surface. Special grinding wheels such as carborundum are not required to shape applicant's cemented carbide tool bits when the tantalum carbide content of such bits is in excess of the tungsten carbide content. However, if the tungsten carbide content is in excess of the tantalum carbide content difiiculty may be encountered in grinding such tools on ordinary emery wheels.

What I claim as new and desire to secure by Letters Patent of the United States, is:

A hard metal sintered composition consisting essentially of from 75-90% tungsten carbide, from 5-25% tantalum carbide, and from 2-20% of a binding metal of the iron group.

FLOYD C. KELLEY. 

